1. Field of the Invention
The invention relates to a driving unit of a welding equipment capable of converting a rotary output of a motor into reciprocating motion of a pressure application shaft so that the pressure application shaft can operate a gun arm or a welding jig.
2. Related Art
There is a conventional driving unit of a welding equipment, as disclosed, for example, in Japanese Patent Laid-Open Publication No. 11-197843. This driving unit of a welding equipment includes a pressure application shaft that is driven by a motor and has a portion to be pulled in the motor, a shaft of a rotor (rotary shaft) of the motor formed of a hollow shaft, a screw shaft fixed inside the rotary shaft at one end thereof, and a nut fixed to the end of the pressure application shaft and screwed with a screw provided in the screw shaft so that the pressure application shaft and the nut are movable on the inner peripheral surface of the rotary shaft.
However, in the conventional driving unit of a welding equipment, since the diameter of the nut fixed to the end of the pressure application shaft is larger than that of the pressure application shaft, the diameter of the rotary shaft or hollow shaft is larger than the diameter of the nut, so that the diameter of the motor becomes larger, and a difference in level is formed between the outer periphery of the pressure application shaft and that of the nut. As a result, bearings of the pressure application shaft can not slide on the portion close to the difference in level therebetween so that a part of the pressure application shaft is not utilized as a direct moving guide part, resulting in increasing the length of the pressure application shaft.